Clionidae

Being a mollusc of mischievous bearing and ghostly aspect, much given to rollicking in a dance at once graceful and deadly. Alongside the Limule they have grown to prominence in the wake of the great cataclysm, spreading as a plague across Abyssea. Of the little that is known about these invertebrates, their proclivity for aggression towards mankind is well-documented.

Historical Background

The clionidae in Final Fantasy XI are based on the animal known as a clione, but they are named (likely accidentally) after a family of sponges.

Clionidae (singular form: clione; plural/scientific name: Clionidae) are a family of mollusks known as sea angels, which are floating sea slugs. They have transparent, gelatinous bodies and propel themselves through the waters of the ocean with "wings" (actually flaps). Small creatures, they rarely get over 2" (5cm) in length. They tend to be found in the cold waters of the Arctic and Southern Oceans, as well as the northern parts of the Atlantic and Pacific Oceans.

Another type of animal known as Clionidae (singular form: clionid; plural form: clionids; scientific name: Clionaidae or Clionidae) are a family of massive sponges.